This invention relates to a system of steel rule die construction that has several advantages over contemporary systems available. There have been many problems in steel rule die construction. In this industry, wood has become the standard die frame material for several reasons. First, it is easy to work with. Most die manufacturers use birch or maple. For structural strength they have traditionally used these woods in multiple laminated layers with opposing grain in order that the wooden structure frame will hold up to constant daylong stress of tonnage pounding on the blades. This wooden frame has been the accepted standard for years as steel rule diemaking is an age old art.
The use of wooden frames has had some advantages over other types of dies. The first major advantage is that they are inexpensive to manufacture. They are also quick to manufacture. Wooden frames are light and easy to store, easy to handle and easy to re-rule. Re-ruling consists of removing the blades after they get worn and replacing them with fresh blades. Once the old blades are removed, re-ruling is essentially the same as installing the blade the first time. However, as the dies are used and blades are removed, the tight fit of the blades inside the wooden frame gets looser and eventually, for dies where the tolerance of the cut is important, the blades fit loose enough that the cut is outside the desired tolerance. At this point, the die frame can no longer be used and a new frame must be constructed.
Here is how wooden die frames are manufactured in a typical situation. First the image is generated on a computer (although some facilities still draw the cut locations with a pencil and ruler)and then the image of where cuts are to be made is printed directly on the wood with a CalComp plotter. Then, typically, the holes are drilled where necessary in the wood as printed by the plotter. Holes are required for structural purposes. Without these holes, the die would fall apart. For example, if blades in a rectangular design were desired and the entire rectangle was cut out in the wood, a wooden rectangle would be removed from the wood. This is undesirable, since this would not hold the blade material in on both sides. So, in order to cut a rectangular groove in the wood, small holes are cut, spaced around one quarter inch apart, called bridges, between which no cut is made. The blade material is notched over this quarter-inch bridge where the blade material in the notch region rests on top of the wooden uncut region, between the one quarter inch holes. The grooves are cut everywhere in the rectangle, all the way through the wood, except between the holes over several such one quarter inch bridges. Then a notched blade is placed in the grooves for the complete rectangle, the notched portions of the rule going in these one quarter inch bridge sections.
In a typical diemaking facility, after the holes are drilled on the wooden frames with the cut-lines drawn on with a CalComp plotter, these holes are used by the jigsaw operator to start cutting the grooves. In the diemaking industry, quick-connect table jigsaws are used and these holes are the connect/unconnect points where the jigsaw blade restarts. The operator of such a jigsaw needs a very good hand and a very good eye, because the skill of the jigsaw operator determines the quality of the steel rule die. Since the thickness of the cut has a tolerance that is very tight, because the blades must fit tight, a jagged cut can in some cases cause a blade not to fit in the groove. The steel rule die manufacturing industry has several standardized blade sizes typically used with precise thickness and precise width. Therefore, the steel rule diemaking business has available different thickness jigsaw blades for each dieblade thickness.
However, if a jigsaw operator is innacurate, one might wind up with a variation in the dimensions of the die from one time to another. This would not be acceptable if a tight tolerance of a specific die is needed. As a result, the computer controlled laser cutting technique has evolved for wooden steel rule die manufacturing. In a typical application for cutting wood dies with great accuracy, a CNC machine controls a laser beam that cuts into the wood. It is used to cut the wooden die-board with computer numerical control. Even the thickness of the cuts may be controlled with great accuracy. Some laser cutter devices of this type use carbon dioxide gas in the laser beam. The gas is pumped into a tube into which the voltage hyperaccelerates causing laser light when the gas is excited to a higher level, thus emitting photons of laser light. Different lasers use different gases such as carbon dioxide, Argon, and other gases. Other laser cutters use different mechanisms. In any case, by using the CNC to control the laser beam, in conjunction with appropriate software, near-perfection may be achieved. Repeatability may be achieved. Most dieboards are at least five eighths of an inch to three quarters of an inch thick. Some are greater in thickness. Because the maximum thickness you may cut "cleanly" with a laser beam using this technique is around three eighths of an inch thick, metal has not been a choice in the board material and the old wood standard has been kept up. However, by using two or more layers of metal, each cut using the same software commands, will be so nearly identical that they may be "layered" to achieve the thickness desired in this invention, as will be seen in a later section. Thus, in this invention, the computer controlled laser may now be used to make metal dieboards, the advantages which will be later pointed out. With this manufacturing technique, a jigsaw operator has been replaced with a laser beam. It is similar to putting a laser beam generator on the calcomp plotter. When the computer controlled laser beam is used, once a pattern is stored in a computer file, it may be reproduced any number of times, and it will generate the same image every time. When using this cutting technique for manufacturing the wooden frames, the one quarter inch spaced "holes" aren't necessary for starting and stopping the jigsaw cut. The one quarter inch bridges of no cut are made without the holes, and thus a die may be manufactured with the same properties as the older style steel rule dies, on wooden frames, but with great precision, duplicability and efficiency.
However, wooden frames have some disadvantages. With wooden frames, there is difficulty splicing the metal blades in the die together without special equipment. For example, a spot welder can splice well without accidentally dulling the sharp blade. But if a normal welder is used by a manufacturer who does not have a spot welder, the normal welder will cause burning in the wooden frame. If one tries to braze or solder the blades when splicing, which is often needed at corners where the metal ends join, the wooden frame can get visible black burn marks. If one has to rebraze in the event of an error on the part of the brazer, then the black burn spot gets more pronounced. When the blades of a die become dull, one may typically rerule the die with fresh blade material. When re-ruling, if one needs to solder again, weld again, or braze again where two blades join, at corners or when spliced, the burn marks will shorten the life of the re-rulability of the frame. Frame life is also shortened by the blades opening the blade slots in the wood wider as the result of many cycles of force or pressure of the blades against the frame during use over time. Some of this may be attributed to wood compression at the rule cut line, causing the rule cut line to widen. When the blade slots in the wood open up and become wider than the blade, the blade might move with respect to the wooden frame and cause an uneven location of the cutting edge of the blade. It also decreases the life of the wooden frame when re-rulability of the frame is desired.
With this minimal ability of joining blades at corners, thicker blades have been required in die design than desired instead of brazing, soldering or welding. If the capability existed of extensive heat-related joining means at the corners where blades join, thinner blades could be used instead of thicker blades. By providing the thinner blades with a strong attachment at the corners, structural strength could be added to the die. Oftentimes, blades are touching. at the corners, just set in place. This requires a heavier than normal blade material which is more expensive, harder to work with (in terms of bending, cutting, and notching) and requires a thicker groove, which significantly adds to the cost, especially of the computer laser beam cut material. The advantage of using thinner blades is that significantly less expensive equipment is required in notching, cutting, and bending. Thinner blades are easier to handle, easier to work with, and put less pressure on the cut frame material. For example, when cutting Lexan polycarbonate plastic using steel rule dies, long narrow pieces may have longitudinal ridges that may be reduced with thinner blade material. The thinner the blade material used in the die, the less pressure the blade makes on the material after the cut, and consequently, less deformity of the material.
The basic equipment used in steel rule assembly is simple. First, a cutting device is used for quick cuts. Second, a bending device is used. Different dies may be used in the bending device to achieve square bends, partially round bends, various arc sizes and other similar bends. Third, an aftercut trimming device called a mitre is often used by a diemaking production line for slightly angling and "aftercut" of the steel rule material. This is done after the cut. The reason this tool is important is because it trims the blade material so that the sharp blade touches the sharp blade in the corners. If there should be a gap on the upper surface where blade does not touch blade, the steel rule die would not make a clean cut and would not operate efficiently. Fourth, a notching tool is used to make quick but precise notches in the structural bottom non-cutting portions of the blade, bridges, usually around one quarter inch long. This tool cuts notches in seconds.
Another problem in steel rule die making is ejection. Generally, rubber or other resilient material is used to eject the material after the cut is performed. The rubber acts like a spring. The part ejects. One problem is that some materials are too hard or too soft fox the application. The choice of the correct rubber is important. However, some of the softer rubbers have the inherent problem that they lose resiliency after being pounded on continuously with tons of force. Consequently, extra labor must be used to replace the rubber on a periodic basis in some cases in the use of steel rule dies. However, it would be even better if the material would "fall through" the steel rule die without requiring rubber replacement and without requiring ejection. Some dies have been developed that have this feature, but these dies are very expensive to make.
Still another problem encountered in the steel rule die industry is that the bottom of the metal blades, the dull side, can tend to move with respect to the wooden frame. When the bottom moves, the cutting edge of the blades no longer are at the same height for cutting. This can cause serious difficulty in performance of the die. One of the symptoms of this problem is uneven cuts and in many cases, not all the blade will cut through the work material when the die is used.